CN110797540A

CN110797540A - Preparation method of gas diffusion layer suitable for high temperature and low humidity

Info

Publication number: CN110797540A
Application number: CN201911067652.6A
Authority: CN
Inventors: 聂颖; 王倩; 陈桂银; 李梦凡; 王强
Original assignee: Sunrise Power Co Ltd
Current assignee: Sunrise Power Co Ltd
Priority date: 2019-11-04
Filing date: 2019-11-04
Publication date: 2020-02-14

Abstract

The invention provides a preparation method of a gas diffusion layer suitable for high temperature and low humidity, which comprises the following steps: preparing a high-conductivity material, a carbon nano tube, a hydrophilic agent and a dispersion liquid into slurry with uniform components in a stirring manner; wherein, the carbon nano tube adopts VGCF-H; uniformly distributing the slurry on the support material in a screen printing mode; and spraying a Nafion solution on the surface of the support material distributed with the slurry by a spraying mode to form the gas diffusion layer. The invention solves the technical problems that the complexity and the energy consumption of a fuel cell system are increased by additionally humidifying in an external humidification or internal humidification mode in the prior art.

Description

Preparation method of gas diffusion layer suitable for high temperature and low humidity

Technical Field

The invention relates to the technical field of fuel cells, in particular to a preparation method of a gas diffusion layer suitable for high temperature and low humidity.

Background

The Membrane Electrode (MEA) is used as a core component of the proton exchange membrane fuel cell and plays a decisive role in the performance of the cell. The Nafion membrane in the MEA needs to have sufficient water to maintain good proton conductivity of the membrane, and the proton conductivity is directly proportional to the water content in the membrane, with higher water content leading to faster proton conductivity and insufficient water content leading to a sharp drop in the proton conductivity of the membrane. Therefore, the key to ensuring stable operation of PEMFCs is to maintain sufficient water content in the Nafion resin in the proton exchange membrane and the catalytic layer. The fuel cell can generate a large amount of moisture in the operation process, but the moisture is generated at the cathode and can be carried away by excessive air, and the moisture can not ensure that the moisture content of the proton exchange membrane is sufficient; therefore, in the current fuel cell technology application, the gas before entering the cell needs to be additionally humidified by adopting an external humidification mode or an internal humidification mode to maintain the humidification degree of the Nafion membrane and the anode catalytic layer, and the additional humidification equipment caused by the humidification needs to increase the complexity and the energy consumption of the fuel cell system, reduce the power density of the fuel cell, increase the cost of the fuel cell, cause a series of problems of difficult hydrothermal management, and seriously obstruct the progress of the commercialization development of the fuel cell.

The patent with the application number of CN105742666A discloses a preparation method and application of a carbon nanotube gas diffusion layer, wherein no water repellent needs to be additionally added on the inner side of the gas diffusion layer prepared by the CVD method, and the carbon nanotubes have strong hydrophobicity, so that the inner side of the gas diffusion layer with carbon nanotubes grown in a concentrated manner has hydrophobicity, the contact angle is 130-150 degrees under the condition of no addition of a hydrophobic binder, and the gas diffusion layer does not need to be additionally added with a water repellent on the inner side and can have good hydrophobic, conductive and mass transfer capacities at the same time.

The carbon nanotube gas diffusion layer prepared in the patent shows anisotropy, and the density of the carbon nanotube vertical to the plane direction of the gas diffusion layer increases from outside to inside; in the direction parallel to the plane of the gas diffusion layer, the carbon nano tube has uniform density, good mass transfer and electric conduction capability, and effectively solves the problem of flooding of the proton exchange membrane fuel cell under high current density.

The gas diffusion layer is prepared by in-situ growth of carbon nanotubes on a macroporous carbon substrate, strong van der Waals force exists among the grown carbon nanotubes, so that the carbon nanotubes are easy to wind and agglomerate after growing, the effective length-diameter ratio of the carbon nanotubes is remarkably reduced, the slippage phenomenon among tubes occurs, and the carbon nanotubes are difficult to uniformly disperse by adopting a conventional dispersion means. The gas diffusion layer prepared by the method of directly adding the carbon nano tube by CVD has unstable performance. The complete process of CVD is relatively complex, various parameters such as carbon source gas, temperature, catalyst, time and the like in the process have great influence on the distribution, the appearance and the structure of the grown carbon nano tube, and the operation repeatability is low. In addition, the surface uniformity of the gas diffusion layer of the carbon nanotube prepared by CVD is poor, so the performance of the prepared MEA is affected by the uniformity.

Disclosure of Invention

According to the technical problems that the external humidification or internal humidification mode adopted in the prior art is adopted to additionally humidify the gas before entering the cell, the humidification degree of the Nafion membrane and the anode catalyst layer is maintained, the complexity and the energy consumption of a fuel cell system are increased, the power density is reduced, the cost is increased, the hydrothermal management is difficult and the like, the preparation method of the gas diffusion layer suitable for high temperature and low humidity is provided. The invention mainly adds a proper amount of VGCF-H and Nafion under the condition that the original ingredients of the microporous layer are not added with a hydrophobic agent and a pore-forming agent, can improve the performance of the MEA under the working conditions of high temperature and low humidity, and is favorable for optimizing the water management capability of the MEA.

The technical means adopted by the invention are as follows:

a method for preparing a high temperature low humidity gas diffusion layer, comprising:

preparing a high-conductivity material, a carbon nano tube, a hydrophilic agent and a dispersion liquid into slurry with uniform components in a stirring manner; wherein, the carbon nano tube adopts VGCF-H;

uniformly distributing the slurry on the support material in a screen printing mode;

and spraying a Nafion solution on the surface of the support material distributed with the slurry by a spraying mode to form the gas diffusion layer.

Further, isopropyl alcohol to which carbon black was added was used as a dispersion medium of the dispersion liquid.

Further, the mass ratio of the carbon black to the VGCF-H is 1:0.5 to 1: 1.5.

Further, the dispersion is a Nafion aqueous dispersion; the content of Nafion in the Nafion water dispersion liquid is 6g to 14 g; nafion acts as a binder for the slurry.

Further, the support material is hydrophobic treated carbon paper; the screen thickness of the screen printing is 20 μm to 50 μm.

Compared with the prior art, the invention has the following advantages:

the invention provides a preparation method of a gas diffusion layer suitable for high temperature and low humidity, which is characterized in that under the condition that original ingredients of a microporous layer are not added with a hydrophobic agent and a pore-forming agent, a proper amount of VGCF-H and Nafion is added; the gas diffusion layer prepared by VGCF has the characteristics of larger aperture and pore volume, and the MEA prepared by the gas diffusion layer not only can improve the performance of the MEA under the high-temperature and low-humidity working condition, but also is beneficial to optimizing the water management capacity of the MEA.

In conclusion, by adding a proper amount of VGCF-H and Nafion under the condition that the original ingredients of the microporous layer are not added with a water repellent agent and a pore-forming agent, the technical scheme of the invention can improve the performance of the MEA under the working conditions of high temperature and low humidity and is beneficial to optimizing the water management capability of the MEA. Therefore, the technical scheme of the invention solves the technical problems that in the prior art, the external humidification or internal humidification mode is adopted to additionally humidify the gas before entering the cell, the humidification degree of the Nafion membrane and the anode catalyst layer is maintained, the complexity and the energy consumption of a fuel cell system are increased, the power density is reduced, the cost is increased, the water heat management is difficult, and the like.

For the above reasons, the present invention can be widely applied to the fields of fuel cells and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic structural view of a gas diffusion layer according to the present invention.

FIG. 2 is a surface topography of a microporous layer according to the present invention.

Figure 3 is a contact angle of a gas diffusion layer according to the present invention.

FIG. 4 is a cell polarization curve of example 1 and comparative example 1 under the high temperature and low humidity conditions of 80 deg.C-RH 60%.

FIG. 5 is a cell polarization curve of example 1 and comparative example 1 under 80 deg.C-RH 40% high temperature and low humidity conditions.

In the figure: 1. a carbon paper substrate; 2. a microporous layer.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. Any specific values in all examples shown and discussed herein are to be construed as exemplary only and not as limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.

In the description of the present invention, it is to be understood that the orientation or positional relationship indicated by the directional terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal" and "top, bottom", etc., are generally based on the orientation or positional relationship shown in the drawings, and are used for convenience of description and simplicity of description only, and in the absence of any contrary indication, these directional terms are not intended to indicate and imply that the device or element so referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore should not be considered as limiting the scope of the present invention: the terms "inner and outer" refer to the inner and outer relative to the profile of the respective component itself.

Spatially relative terms, such as "above … …," "above … …," "above … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial relationship to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary term "above … …" can include both an orientation of "above … …" and "below … …". The device may be otherwise variously oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

It should be noted that the terms "first", "second", and the like are used to define the components, and are only used for convenience of distinguishing the corresponding components, and the terms have no special meanings unless otherwise stated, and therefore, the scope of the present invention should not be construed as being limited.

Example 1

The invention provides a preparation method of a gas diffusion layer suitable for high temperature and low humidity, which comprises the following steps:

the Nafion solution is sprayed on the surface of the supporting material distributed with the slurry in a spraying mode to form a gas diffusion layer, the gas diffusion layer with a special pore structure and proper hydrophilicity and hydrophobicity is formed, the gas diffusion layer has the characteristics of large pore diameter and large pore volume, so that the gas diffusion layer has certain advantages in water retention, the wetting of the proton exchange membrane can be well kept, gas can be better contacted with a catalyst, and the electrical property of the MEA is also improved.

Further, the mass ratio of the carbon black to the VGCF-H is 1:0.5 to 1: 1.5.

Further, the support material is hydrophobic treated carbon paper; the screen thickness of the screen printing is 20 μm to 50 μm. The paste has low viscosity, is also suitable for a screen printing coating mode, and needs to control the thickness of the paste penetrating into the carbon paper.

The preparation method provided by the invention has the advantages of simple operation process, less variety of required raw materials and low equipment requirement.

The carbon nanotubes used in the present invention are usually CNT, CF, VGCF-H, etc., and the carbon nanotubes used in the present invention are VGCF-H. The carbon nano tube has hydrophobicity, a hydrophobic agent does not need to be added after the microporous layer contains the carbon nano tube, the contact angle range of the MPL of the microporous layer is 150-170 degrees, the hydrophobicity influences the discharge rate of the generated water, and the hydrophobicity of the MPL is determined according to the operation condition of the proton exchange membrane fuel cell.

When preparing MEA, the gas diffusion layer GDL does not need to be roasted, the proton exchange membrane (CCM) coated with the catalyst, the gas diffusion layer and the polyester frame are prepared into the MEA in a pressing way, and the pressure intensity in the pressing process is 40kg/cm²-100kg/cm²。

Further, observing or testing the gas diffusion layer prepared by the method of the invention, then preparing the MEA by using the gas diffusion layer and testing the performance, wherein the specific operation process is as follows:

1) diluting the Nafion concentrated solution with the mass fraction of more than 5% to 5% by using deionized water, and uniformly stirring;

2) 3g of carbon black, 1g of VGCF-H and 13.16g of 5 percent Nafion water dispersion are weighed and poured into a certain amount of isopropanol, and the mixture is uniformly stirred to prepare slurry with the viscosity of 80-150 cp;

3) coating the slurry on hydrophobic carbon paper by adopting a screen printing method to form a microporous layer with the coating thickness of 20 mu m;

the schematic structure of the prepared gas diffusion layer is shown in fig. 1;

4) observing the surface topography of the microporous layer of the gas diffusion layer, as shown in figure 2;

5) carrying out roughness test on the surface of the microporous layer; wherein, comparative example 1 is the diffusion layer produced by the prior art, VGCF is not added to the slurry in the experimental process, all the proportions are carbon black, and the total amount is the same; no Nafion is added, PTFE is used for replacement, the using amount is the same, and other process parameters are the same as those in the embodiment 1; the test results are shown in table 1;

TABLE 1 surface roughness test results for microporous layer

Sample name	Interfacial developed area ratio	Maximum height difference (mum)
			Comparative example 1	4.013	63.7
Example 1	3.163	57.44

6) The prepared gas diffusion layer, CCM and polyester frame are added by an oil press to 100kg/cm²Is pressed into an effective reaction area of 25cm²MEA (2 pieces in total);

7) assembling the rest 1 of the MEA prepared in the step 6) into a single cell, and carrying out initial performance test; the schematic structure of the single cell is shown in FIG. 3; the test device is a 850e-885 fuel cell test system, the polarization curve of a single cell is tested, the result under the condition of 80 ℃ RH 60% is shown in figure 4, and the result under the condition of 80 ℃ RH 40% is shown in figure 5.

And (3) observing and testing results:

as shown in FIG. 1, a hydrophobic carbon paper substrate 1 with large pore size is subjected to micropore screen printing of a slurry added with VGCF-H carbon nanotubes to form a micropore layer 2 with large pore size and large pore volume.

As shown in fig. 2, it can be seen from the surface topography of the microporous layer that the surface of the microporous layer of comparative example 1 is flat and dense after the carbon nanotubes are added, and most cracks and pits of the microporous layer disappear.

As shown in table 1, the thicknesses of comparative example 1 and example 1 are similar, the interfacial spreading ratio and the maximum height difference of the sample surface were obtained by using the surface roughness tester, and the test values did not change significantly under the condition of similar thicknesses.

As shown in fig. 3, it is understood from the contact angle results of the gas diffusion layer obtained by the experiment that the surface of the gas diffusion layer to which the carbon nanotubes are added shows hydrophobicity without adding the hydrophobizing agent.

As shown in fig. 4, the electrical properties of the single cell polarization curves of example 1 and comparative example 1 under high temperature and low humidity conditions (80 ℃ -RH 60%) are shown: in the case that the total thickness of the microporous layers of comparative example 1 and experimental example 1 is consistent, the proton exchange membrane fuel cell composed of the gas diffusion layer added with the carbon nano tube has better performance, the water retention capacity of the low-electric density area is better than that of the comparative example, the water management capacity is improved, and the mass transfer performance of the MEA can be improved.

As shown in fig. 5, the electrical properties of the single cell polarization curves of example 1 and comparative example 1 under high temperature and low humidity conditions (80 ℃ -RH 40%) are shown: the working condition humidification is continuously reduced, and the proton exchange membrane fuel cell composed of the gas diffusion layers added with the carbon nano tubes has better performance and obvious water management capability advantage under the condition that the total thicknesses of the microporous layers of the comparative example and the experimental example are kept consistent, and can improve the mass transfer performance of the MEA.

The single cell polarization curves of example 1 and comparative example 1 show that the gas diffusion layer with a microporous layer structure added with a certain amount of VGCF-H has certain water retention under the working conditions of high temperature and low humidity, and can effectively improve the electrical property of the proton exchange membrane fuel cell within a certain humidity range.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a gas diffusion layer suitable for high temperature and low humidity is characterized by comprising the following steps:

2. The method for preparing a high-temperature low-humidity gas diffusion layer according to claim 1, wherein the dispersion medium of the dispersion liquid is isopropyl alcohol to which carbon black is added.

3. The method for preparing a high-temperature low-humidity gas diffusion layer according to claim 2, wherein the mass ratio of carbon black to VGCF-H is 1:0.5 to 1: 1.5.

4. The method for preparing a high-temperature low-humidity gas diffusion layer according to claim 1, wherein the dispersion is an aqueous Nafion dispersion; the content of Nafion in the Nafion water dispersion liquid is 6g to 14 g; nafion acts as a binder for the slurry.

5. The method for preparing a high-temperature low-humidity suitable gas diffusion layer according to claim 1, wherein the support material is a hydrophobically treated carbon paper; the screen thickness of the screen printing is 20 μm to 50 μm.